Download Unit 4 Photosynthesis

UNIT 5
PHOTOSYNTHESIS
ENERGY & MATTER
Energy
In – Sunlight
Out – Bonds between Biomolecules
Matter
In – H2O(Soil; van Helmont), CO2 (Air), Inorganic
Inorganic – No Carbon
Organic - Carbon
Out
O2; Other Biomolecules (Sugars, ETC.)
QUESTION…
Where does photosynthesis occur?
ANATOMY OF PHOTOSYNTHESIS
Leaf
Major site of photosynthesis;
although can occur all over Plant
Mesophyl – tissue in interior of leaf
Stomata – Pores; take in CO2 release O2
Vein – Transport water absorbed by roots
Chloroplasts
Organelle of photosynthesis
 2 membranes;
 Thylakoids – houses light absorbing pigments



thylakoid sacs are stacked – named Granum
Stroma & thylakoid space
CHLOROPHYLL & PIGMENT
Chloroplasts are BOUND DIRECTLY to thylakoid
membrane
Provide thylakoid with its “green” color
What is a pigment?
Substances that absorb visible light
- Different pigments absorb different wavelegnths of
light
Light can be reflected, transmitted, absorbed
Whiteboard?
Tabletop?
Leaf?
PHOTOSYNTHESIS
Complex set of reactions that convert light energy into
chemical energy.
Three types of Energy Conversions
1. Light absorption
2. Conversion of Light Energy into Chemical Energy
3. Storage of Chemical Energy as sugars
-
1 & 2 make up what we call the
Light (dependent) Reactions
-
-
Convert to energy; Photo portion
3 is a process known as
Light Independent (Dark) Reactions

AKA - The Calvin Cycle
Build biomolecules
DIAGRAM – LIGHT REACTION
Two clusters of light absorbing pigments:
Photosystem II
Photosystem I
Named in order discovered
Regions of Concentrated Chlorophyll
What is evidence that red and blue light is absorbed in
plants?
In absorbing light, what change does this cause?
Energized electrons leave chlorophyll
Move down proteins by Electron Transport
Chain
Any time molecule ACCEPTS electrons
Reduced or Oxidized?
REDUCED
Oxidation
Is
Loss (e-)
Reduction
Is
Gain (e-)
Rapid shift down proteins: Reduced  Oxidized 
Reduced…
REDOX REACTION
This process is how electrons move down proteins of
Electron Transport Chain
OVERVIEW QUESTIONS
What do we know about the structure of a leaf?
What are the names of the reactions that occur
during photosynthesis?
How would you describe what occurs in the Light
Reactions?
How would you describe what occurs in the Light
Independent Reactions/Calvin Cycle?
When pigment molecule absorbs a photon, photon is
passed from protein to protein
Electron Transport Chain

Think of “The Wave”
Series of protein molecules embedded in thylakoid
membrane
 @ Each protein



Redox reactions – pass e-
Small amount of energy is released from each Redox
reaction
Certain proteins serve only to pass eOthers have specific function
When e- passes through a specific protein in ETC
Causes the ACTIVE TRANSPORT of H+ into
Thylakoid space

Like PSII & PSI, proteins in ETC are embedded in
thylakoid membrane
Surplus of protons (H+) develop within the interior
of Thylakoid – Set up HUGE Concentration
Gradient

More H+ on the interior than on the exterior
Is the movement of H + this active or passive
transport?
Do we need a transport protein?
Is this energy requiring or energy releasing?
How does this energy change our system?
Helps form ATP!!!
ATP
Known as
Adenosine Triphosphate
Structure:
The process of using energy – running metabolism
Break ATP into
Adenosine Diphosphate
Structure:
Run reactions for energy –
Which is energy storing? LR or RL
Energy releasing?
This whole process has a specific name:




Movement of protons within the thylakoid space
due to the redox reactions that move electrons
down the Electron Transport Chain
H+ Gradient develops
Ion Channel – ATP Synthase moves H+ out of the
thylakoid
Provides energy for the formation of ATP from
ADP + P + Energy
Chemiosmosis
PHOTOSYSTEM I
95% of what we know about PSII are the same for
PSI
 Photons hit chlorophyll A & B
 Excite electrons to a higher energy state
 Electrons are accepted by proteins in ETC,
“jump” from protein to protein
 Cause influx of H+ into thylakoid space

Will help “power” ATP Synthase
5 % DIFFERENCE
1. Electrons from PS II are OXIDIZING PS I

Refilling e- lost at PS I
Photons hit PSI, excite process
2. Electrons from PSI reduce NADP+
NADP+ is the final “resting place” – of e• Final electron acceptor
VERY High affinity for electrons
PHOTOSYSTEM I
At end of the reaction:

NADP+ + H+ + 2e- _________> NADPH
NADPH is known as a Coenzyeme
“Electron shuttle”
 Accept electrons – transfer to different source
 Pick up electrons, transfer them to Calvin Cycle,
return to Light Reaction

PHOTOLYSIS
Specific enzyme is attached to PSII that breaks
H2O down


Occurs simultaneously as photons are hitting
PSII
Light splits H2O
4 H+
 4 e O2

What are the functions of all of the above?
3CO2
(3) 5-Carbon
Ribulose
BiPhosphate
RuBP
3 ADP
(3)
6-Carbon
Intermediate
- Unstable
3 ATP
(6) 3-Carbon
PGA
(5) 3-Carbon
PGAL
6 ATP
6 ADP
(6) 3-Carbon
PGAL
(1) 3- Carbon
PGAL
6 NADPH
6 NADP+
(3)
6-Carbon
Intermedia
te
- Unstable
(3) 5-Carbon
Ribulose
BiPhosphate
PGA
(6) 3Carbon
(5) 3Carbon
PGA
PGAL
(6) 3Carbon
PGAL
GOALS
1.
Compare and contrast the advantages and
disadvantages of the following:

C3, C4 & CAM
2.
Explain how limiting factors (CO2, O2, Light,
H2O) may affect photosynthesis and be able to
draw/explain graphs that detail various limiting
factors
3.
Predict how photosynthesis will change when
environmental factors change
ENVIRONMENTAL EFFECTS
OF PHOTOSYNTHESIS

Goal is to examine various environmental effects
that implications on the rate of photosynthesis
RETURN TO ANATOMY
How do plants move CO2 & H20 in and O2 out of
the plant?
Stomata
 pores on the underside
 Exchange CO2, H20 and O2
 Has the ability to close - Guard Cells
PHOTORESPIRATION


When RUBISCO binds to O2 instead of CO2
Although RUBISCO is efficient of binding inorganic
carbon (CO2) – it also attracts O2 to binding site
O2 and CO2 have SIMILAR SHAPE
 Non-specific active site

4x higher binding affinity for CO2 than O2

Running photorespiration lowers photosynthetic output
Takes in O2, Releases CO2
 Only one PGAL per cycle

Half as efficient!
PGA
PGA
PHOTORESPIRATION – EVOLUTIONARY
RELIC

At point of origin of photorespiration, there was NO O2
in the atmosphere

Why should we consider this?
2.5 to 3 BILLION years ago – environment was almost
all CO2
Unnecessary for plants to worry about O2 binding
Not much O2 in the atmosphere,
 no need for enzyme to differentiate between O2 and CO2

Inefficient?
Adaptation to address the inefficiency?
C4
C3 STRUCTURE VS. C4 STRUCTURE
C4
What do we need to address the inefficiency of Rubisco?
A different enzyme to avoid O2 binding.
We got it –
PEP Carboxylase
Fixes CO2 to 3C structure PEP
to form 4C OAA - Oxaloacetic Acid
Various Enzymes convert OAA into 4C Malic Acid
Malic Acid “sneaks” CO2 into Bundle Sheath Cells
CO2 Breaks off – Run Calvin Cycle as Normal
C4
EXTREMELY IMPORTANT
THE BUNDLE SHEETH CELLS ARE
IMPERMEABLE TO CO2!!
Why is this important?
Carbons are really stow-aways
Move 4th Carbon into bundle sheath cell
 Separate from Malate – Malate leaves – NOT CO2
 Once in, cannot leave

Thus C4 concentrates CO2 in Sheath Cells
Examples of C4 Plants:
Rice, Soybeans, Sugar Cane, Corn Warm Season Grasses
C4 ADVANTAGE
C4 more effective in High Temperatures or High O2
environments
What happens in environments w/ high temp.?
Stomates Close
Mesophyll cells “pump” CO2 into the bundle sheath cells,
 Continuously keeping CO2 concentration high
Avoid possibility for Photorespiration
C4 plants are successful in hotter/drier climates –
C4 DISADVANTAGE
More ATP required to convert 3-Carbon in
Sheath cell back into PEP
Spend extra energy to run this reaction.
Need PEP to bind CO2 to OAA

Must spend energy to convert pyruvate into PEP
The question is –
How does the carbon fixation of C3 differ from
C4? (aside from process…)
LOCATION, LOCATION,
LOCATION!!!
CAM
CAM – Crassulacean Acid Metabolism
 Adaptation for intense arid conditions

Many succulent plants, cacti, pineapples, Jade


Plants open stomata at night


Water conservation adaptation
Take up CO2 & incorporate into organic acids
Close stomata during the day
Prevent massive water loss
 But, no CO2 can enter

CAM

During the day, when light is plentiful CO2 is
released from Organic Acids
Breaks off of Malic Acid
 CO2 moves to Calvin Cycle


Organic Acid returns to bind more CO2 at night
So, how do C4 and CAM pathways of carbon
fixation differ?
C4 Separates Calvin Cycle in LOCATION
CAM separates Calvin Cycle in TIME